not a problem at all . I did that last december , and no problems at all . The bike is not written down in your passport , and in Mali they seldom ask for the passavant .
I actually told the passports/douanne people that I left a bike in Mali for a few months and they couldnt care less !.
your only problem is that when you are back then your passavant is probbably expired , and then you "could" have a problem , as they "could" charge you whichever ammount of money to get you a new fresh passavant .
Alternatively , and being in my ussual line , I didnt care at all , drove all around Mali without a Passavant *nor insurance* at all , and the only checkpoint that they asked me , I chatted my way out of the trouble with a big smile , a few handshaking , and digital pictures here and there.
Have a nice day.